Extrusion apparatus

ABSTRACT

An apparatus is provided for the extrusion of polymer products from a pool of molten polymer. The apparatus is comprised of at least two movable die members between which the polymer is extruded. The moveable die members apply pressure to the surface of the extruding sheet to spread and smooth out gauge variations in the extruded product to reduce the visual effects of the gauge variations on the extruded sheet.

United States Patent 1191 Larsen Feb. 5, 1974 EXTRUSION APPARATUS [75]Inventor: Ronald L. Larsen, Minneapolis,

Minn.

[73] Assignee: Conwed Corporation, St. Paul,

Minn. 1

22 Filed: Nov.26, 1971 211 App1.No.:202,451-

Related US. Application Data [62] Division of Ser. No. 47,755, June 19,1970.

52 US. Cl 425 325, 425/224, 425/340, 425/394, 425/461, 264/176, 264/21051 Int. Cl. B29d 7/02 [58] Field of Search.... 264/176, 210, 175;425/325, 425/71, 328, 72, 385, 224, 461, 363, 175, 340

[56] References Cited UNITED STATES PATENTS 1,603,812 10/1926 Stein..264/175X Loomie 425/72 X 3,526,927 9/1970 Villain 425/71 3,543,33312/1970 Anders et a1. 425/141 2,715,256 8/1955 Siegrist 425/4612,804,651 9/ 1957 Peterson 425/461 X 2,791,801 5/1957 .Szantoy.....425/72 X 3,504,075 3/ 1970 Williams 264/175 Primary Examin'er-RobertI... Spicer, Jr. Attorney, Agent, or Firm-Eyre, Mann & Lucas 1 1ABSTRACT An apparatus is'provided for the extrusion of polymer productsfrom a pool of molten polymer. The apparatus is comprised of at leasttwo movable die members between which the polymer is extruded. Themoveable die members apply pressure to the surface of the extrudingsheet to spread and smooth out gauge variations in the extruded productto reduce the visual effects of the gauge variations on the extrudedsheet.

8 Claims, 5 Drawing Figures EXTRUSION APPARATUS This application is adivision of Ser. No. 47,755, filed June 19, 1970.

This invention relates to method and apparatus for the extrusion ofpolymer products and more particularly to apparatus and method forproducing a sheet of polymer in which gauge variations on the'sheet arecontrolled.

In accordance with the present invention, two or more relativelymoveable die members are provided between which molten polymer underpressure is extruded. Each of the moveable die membersis adapted to moveon and resist the-pressure force of the surface of the extruding sheetwhile the sheet is still molten polymer to reduce the variations insheet planar thickness or gauge variations normally caused by variationsin the die member lands to maintain uniform'sheet thickness only withinthe pressure force limits. Conventional extrusion apparatuses generallyprovide two stationary die members forthe extrusion'of a sheet ofpolymer. Any irregularities in the die lands of the conventionalapparatus will appear as a high or low spot or ridge on the extrudedsheet of polymer. These irregularities on the surface of the sheetappear in a rather constant position on the surface thereof which makesthe sheet appear wavy, especially when the sheet is wound up on a roll.By extruding sheet between relatively moveable die members as providedfor in the instant invention, these irregularities or gauge variationswill be spread across the sheet or smoothed out to give the sheet a muchmore uniform appearance.

It has been found that for best results, only a portion of the diemembers are made moveable on the surface of the sheet. By reducing themoving surface area in contact with the polymer sheet, the shear stressapplied to the extruding polymer is reduced. To achieve this beneficialreduction in shear stress, the die members are provided with moveabledie lips between which the sheet is extruded and the remaining portionof the die members are not moved on the surface of the sheet. Thedielips or die members as the case may be may be moved at any speed butpreferably they are moved at the extrusion speed to prevent the moveabledie lips from interfering with the extrusion process. Of course, the diemembers or the die lips may be moved faster or slower than the extrusionspeed to give the sheet various decorative effects if this is desired.Although in most cases the die members on either side of an extrudingsheet will be made moveable to control gauge variations on both sides ofthe sheet, only one die member need be made moveable if control of gaugevariations on only one side of the sheet is desired.

For best results, the die members are moved on the surface of theextruding sheet either in the direction of extrusion or transversethereto to prevent unduly increasing the pressure necessary forextrusion. Also for best results, the moveable die lips areheated to atemperature equal to the melt temperature of the polymer being extrudedso that gauge variations in the sheet may be easily smoothed down by themoving die lips.

Of course, the die members may be moved in conventional manner toincrease or decrease the space between die members to produce adifferent thickness sheet.

The moveable die lips of the instant invention may be provided withsurface designs thereon or with means for cutting into the sheet toproduce a particular pattern effect. Depending on the type of patterndesired,.

' of the film is to be continuously cut, a temperature equal to orhigher than the melt temperature will be used to facilitate the easyremoval of polymer from the sheet. If a pattern is to be impressed intothe sheet, a temperature equal to and preferably below the melttemperature will be used to prevent polymer form flowing back into theimpressed design and to prevent the compressed polymer from springingback to its original shape. It is well within the skill of the art todetermine the particular temperature necessary. to properly impress orcut any design into the surface of the sheet being extruded.

Referring now to the drawings wherein various preferred embodiments ofthe invention are depicted and wherein like numerals refer to like partsFIG. 1 is a side sectional view of one embodiment of the apparatus madein accordance with the instant invention.

FIG. 2 is an isometric'schematic view of a sheetextruded by an apparatuswithout the moveable die members of the instant invention.

FIG. 3 is a side view of another embodiment of an apparatus made inaccordance with the present invention.

FIG. 4 is a side view of still another embodiment of an apparatus madein accordance with the present invention.

FIG. 5 is yet another embodiment of an apparatus made in accordance withthe present invention.

Referring now to FIG. 1, there is seen an extrusion die 10 which iscomprised of two die members 12 and 14. Die members 12 and .14 receivepolymer from a conventional screw extruder (not shown) through channel16 which channel terminates in a flow regulating manifold 18. Manifoldl8 spreads the polymer into a uniform flow across the entire land area20 of the die members.

Mounted at the end of die members 12 and 14 are a pair of moveable rolls24 and26 respectively. Rolls 24 and 26 are spaced apart a distance equalto the distance between lands 20 as indicated by arrow 22 and it isthrough these moveable rolls that the sheet of polymer such aspolypropylene is extruded. The rolls 24 and 26 are rotated byconventional means (not shown) such as a standard torque motor in thedirectionof the arrows 28 in FIG. 1. For best results, the direction ofrotation of the rolls 24, 26 coincides with the direction of extrusionto avoid the application of shear forces on the extruded polymer in adirection opposite to extrusion. The rolls need not be motor drivenalthough best results are achieved when the rolls are motor driven sincethe speed of rotation can then be controlled and adbanding thereon asshown at 32 in FIG. 2. Numeral 32' represents a raised band of polymerin the extrusion direction which results from imperfections in dieconstruction or imperfect adjustment of the die lips or the gaugevariations may result from an. imbalance in the extrusion system whichtends to occur from time to time. As the sheet passes between rolls 24and 26, the imperfections are varied by rotation of the rolls to avoid acontinuous band in one location. ln the case of intermittent gaugevariations, the moveable rolls will tend to move these in the extrusiondirection to smooth out the high spots in the sheet. When the sheet iswound up on a roll, the sheet will not appear as wavy as it will whenthe high spots have not been reduced in accordance with the presentinvention. For best results, the rolls are heated by conventional means(not shown) which may take the form of electric wires in the rolls or bya supply of hot oil to the interior'of the rolls. Conventionalthermostat means (not shown) may be used to control the temperature ofthe rolls 24 and 26.

The apparatus depicted in FIG. 3 is exactly the same as that depicted inFIG. 1 except that the moveable rolls 24 and 26 are replaced by a pairof endless rotating belts 34 and 36. These endless belts are mounted forrotation on a plurality of rollers 38 which may be driven byconventional means (not shown). The belts 34, 36 may be made of steel orany relatively still material capable of withstanding the hightemperature of the extruded polymer and of resisting pressure of themelted polymer to change and spread the gauge variations appearing inthe sheet.

The apparatus depicted in FIG. 4 is essentially the same as that shownin FIG. 3 except that the belts 34 and 36 rotate in a directiontransverse to the direction of extrusion. Moving the belts in adirection transverse to the direction of extrusion tends to spread gaugevariations' on the sheet across the complete width of the sheet thusproviding for a much more uniform appearing thickness sheet.

The apparatus depicted in FIG; is essentialy the same as that shown inFIG. 4 except that the rotating die lips have been replaced byreciprocating bars 40, 42. The reciprocating bars move in oppositedirections to each other and apply a cntinous force to the surface ofthe extruded sheet substantially to removethe gauge variationstransversely across the sheet.

In all of the embodiments shown, the moveable lips may have a designimpressed thereon which design is imparted to the extruded sheet. Inaddition, only one moving member may be used and the die lip on themember opposite the die member containing the moveable member may beextended to support the sheet until the sheet has been extruded frombetween the moveable lip and the land of the extended die member.

lt is intended to cover all modifications of the embodiments hereinchosen for the purposes of illustration which do not constitutedepartures from the spirit and scope of the invention.

What is claimed is:

1. An apparatus for controlling gauge variations on a sheet of polymercomprising:

a. two die members approximately uniformly spaced apart over asubstantial length thereof for forming melt extrusion of a desired gaugesheet of molten polymer;

b. two spaced heated, continuously moving members disposed immediatelyadjacent the uniformly spaced length of the die members, each of whichis immediately adjacent one of said uniformly spaced die members;

c. the space between the continuously moving members being essentiallyequal to the uniform space between the die members;

d. the continuously moving members beingdisposed to contact and act onthe sheet surface of the sheet of polymer while it is still molten fromextrusion and before it has set to reduce the variations in the sheetplanar surface to maintain uniform sheet thickness only within themoving members limit; and

e. the temperature of the contacting surface of said continuously movingmembers being approximately equal to the temperature of the moltenpolymer sheet.

2. The apparatus of claim 1 wherein the continuously moving members movein the direction of extrusion.

3. The apparatus of claim 2 wherein the continuously moving members arerolls.

4. The apparatus of claim 2 wherein the continuously moving members arebelts.

5. The apparatus of claim 2 wherein the continuously moving member ismoved at the same rate as the speed of extrusion of the polymer sheet.

6. The apparatus of claim 1 wherein the continuously moving members movein a direction transverse to the direction of extrusion.

7. The apparatus of claim 6 wherein the continuously moving members arebelts.

8. The apparatus of claim 6 wherein the continuously moving members arebars.

I! l 1.! I. I

1. An apparatus for controlling gauge variations on a sheet of polymercomprising: a. two die members approximately uniformly spaced apart overa substantial length thereof for forming melt extrusion of a desiredgauge sheet of molten polymer; b. two spaced heated, continuously movingmembers disposed immediately adjacent the uniformly spaced length of thedie members, each of which is immediately adjacent one of said uniformlyspaced die members; c. the space between the continuously moving membersbeing essentially equal to the uniform space between the die members; d.the continuously moving members being disposed to contact and act on thesheet surface of the sheet of polymer while it is still molten fromextrusion and before it has set to reduce the variations in the sheetplanar surface to maintain uniform sheet thickness only within themoving members limit; and e. the temperature of the contacting surfaceof said continuously moving members being approximately equal to thetemperature of the molten polymer sheet.
 2. The apparatus of claim 1wherein the continuously moving members move in the direction ofextrusion.
 3. The apparatus of claim 2 wherein the continuously movingmembers are rolls.
 4. The apparatus oF claim 2 wherein the continuouslymoving members are belts.
 5. The apparatus of claim 2 wherein thecontinuously moving member is moved at the same rate as the speed ofextrusion of the polymer sheet.
 6. The apparatus of claim 1 wherein thecontinuously moving members move in a direction transverse to thedirection of extrusion.
 7. The apparatus of claim 6 wherein thecontinuously moving members are belts.
 8. The apparatus of claim 6wherein the continuously moving members are bars.